This invention is directed to an automotive suspension system and involves a piston-type apparatus for enabling a user to vary vehicle suspension roll stiffness, automatically or manually, between either of two pre-defined levels (with and without an anti-roll bar) whereby to control the ride and handling characteristics of the vehicle.
This invention provides vehicle suspension apparatus to achieve one or more of the following objectives. A primary objective in a multi-purpose vehicle can be to reduce roll stiffness from a nominal highway setting to a rough-road or off-road setting in order to improve rough-road and off-road ride comfort; improve off-road mobility; and improve vehicle durability by reducing rough-road and off-road induced structural stress. Another objective can be to increase roll stiffness in full payload condition in order to maintain more consistent ride and handling properties across wide range of payload variation. A third objective may be provision of apparatus by which the roll stiffness distribution between the front and rear suspensions can be adjusted statically or dynamically in order to modify or maintain handling characteristics.
In accordance with this invention, a suspension system for a motor vehicle comprises two largely vertical coupling links adapted to be connected between ends of an anti-roll bar which is pivoted on the vehicle chassis (i.e., the sprung mass) and respective road wheel suspension linkages at opposite sides of the vehicle (i.e., the unsprung masses), one coupling link being a conventional rigid tie rod and the other coupling link being a hydraulic piston and cylinder assembly, hereafter referred to as a hydraulic link. The rigid tie rod is axially inextensible and has its opposite ends pivotably connected, respectively, to one reaction end of a conventional torsional anti-roll bar and to the suspension linkage of one of the front wheels (i.e., a suitable reaction point on the suspension).
The hydraulic link is manually or automatically locked or allowed relative axial motion, and comprises a cylinder having opposite end walls and a port adjacent each end wall, and a piston carried by an actuator rod. The actuator rod comprises a first and second piston rod, each piston rod having its axis concentric with the cylinder axis and protruding from one respective end wall. The cylinder and one piston rod from the piston are connected, respectively, to the other reaction arm of the anti-roll bar and to the axle of the other wheel (or to a symmetrical reaction point, across the suspension) or vice versa. The piston rods are of equal cross-section and length. Hence, contrary to a shock absorber wherein the piston rod extends from one face of the piston, the swept, or displaced fluid volume per unit axial travel is the same on both sides of the piston.
Hydraulic switching to allow substantially incompressible fluid to flow from one port to the other port is preferably achieved by a normally closed solenoid valve or other remotely activated poppet valve(s). The operation is passive (no substantial power required). Further, should the valve be closed, for whatever reason, and the piston displaced from center, fluid by-pass arrangements are provided to allow the piston to stabilize (and be locked against further motion) centrally of the cylinder. In accordance with this invention, axial grooves on the inner wall of the cylinder, or other secondary fluid passages, are provided in order to allow the piston to center and automatically remain locked in this position.
Advantageously, the automotive suspension system herein provides an apparatus and method of varying suspension roll stiffness between a first harder suspension roll mode and a second softer suspension roll mode.
Advantageously, the suspension system herein will allow control of suspension roll stiffness for conditions during on-road and high speed driving wherein the hydraulic link is "locked", and during off-road and low speed conditions wherein the hydraulic link is "unlocked" for uncoupling the anti-roll bar from the suspension.
Advantageously, the hydraulic link apparatus herein will tend to return to a "piston locked" mode in the instantaneous zero roll position of the suspension after the manually or automatically controlled valve has disconnected the main flow path between the two sides of the piston.
The foregoing and other objects, and advantages, will become more apparent when viewed in light of the accompanying drawings and following detailed description wherein: